Holocaust denial and racial abuse on public transport could be allowed in Australia under proposed changes to the Racial Discrimination Act, Greens MLA Shane Rattenbury has warned.

Removing section 18c of the act could also cause the country's repution abroad to suffer, akin to the fallout from the 2005 riots at Cronulla, violence against Indian students in Melbourne and the nation's treatment of asylum seekers.

In a submission responding to an exposure draft released by Attorney-General George Brandis, Mr Rattenbury argues repealing clauses that make it illegal to "offend, insult, humiliate or intimidate" on the grounds of race would set back Australia's multicultural progress.

The changes have received wide-ranging and sustained criticism, including from some government MPs and cultural and religious groups around Australia.

Mr Rattenbury plans to seek amendments to the ACT's own Discrimination Act to outlaw the behaviour if the Commonwealth changes go ahead.

He said the current laws placed only a minor and justifiable limitation on free speech and concerns were "hyperbolic and unwarranted".

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"My view is that if the changes are introduced and passed, they will not result in any increase in genuine and constructive free speech in Australia," Mr Rattenbury said in the four-page submission.

"However, they will 'dog-whistle' to an unattractive underbelly of racism, promoting behaviour that will erode tolerance and harmony in Australia and cause significant mental, psychological and possible physical suffering to ethnic and religious minorities."

A proposal measuring the effect of the act to be determined by the standards of a reasonable member of the community defeats the purpose of discrimination provisions, he argued.

"Imagine if our sexual harassment laws said that whether something was sexual harassment was not to be determined with reference to a particular gender; it does not make sense given the reality of gender relations that inform sexual harassment," the submission states.

University of New South Wales constitutional law expert George Williams said existing clauses in the federal law had preserved the ability of states and territories to pass laws that further limit racist behaviour.

Mr Rattenbury believes the laws could operate concurrently.

Before the exposure process last week, Chief Minister Katy Gallagher signalled she would make a submission to the Attorney-General's Department on the draft.

Mr Rattenbury said he does not oppose the introduction of concepts including vilification and intimidation into the act but argues they are not an adequate replacement for the section proposed to be withdrawn.

"The Australian community, and the Australian government, have put a large amount of effort and resources into improving community harmony over many years," he said.

"Changing the existing RDA racial hatred provisions in the way proposed will remove a keystone of this work."